“Generally, what you find is during the morning you get a build-up in the peak hour – when it’s cold you get poor dispersion and dilution,” he said. “When it warms up you get more mixing and it goes up higher, rather than getting trapped, and at night it comes down again.”

For that reason, air quality is generally slightly worse in winter.

Mr Torre said it was only about seven days last year that the air quality in the CBD exceeded the standard. In Alphington, for example, there were eight days – probably because of more wood fired heating in the suburbs.

But the biggest negative influence on air quality in the inner city are bush fires and planned burns from out of Melbourne.